Conventional tractor-trailer truck landing gear mechanisms are generally used to level and to support heavy trailers in the absence of the tractor which normally supports the front end of the trailer. The conventional landing gear mechanism is usually operated by a handle attached to one end of a rotatable shaft. A gear mechanism transmits such rotational movement of the handle to a pair of telescoping legs, for extending or retracting the landing gear mechanism. The extension or retraction of the landing gear mechanism is also used for coupling or uncoupling a fifth wheel used for coupling the tractor and trailer.
Such manual operation of the landing gear mechanism, however, has proven to be less than satisfactory in that it is relatively dangerous, slow, awkward, difficult, expensive, exhausting and time consuming to operate. In this respect, and as illustrated in U.S. Pat. No. 1,093,590, the conventional landing gear mechanism includes rotatable teeth for engaging a gear device, to cause the desired extension or retraction of the telescoping legs. The frequent use of the landing gear mechanism, however, and the heavy weight supported thereby, can cause the teeth to wear, and eventually to fracture, thereby causing the supported structure to collapse inadvertently. In which event, the operator is generally required to report the incident to the highway authorities, and to restore the trailer to a levelled position with a crane or the like. Such unwanted and undesirable event is costly and time consuming.
As exemplified by the following U.S. Pat. Nos. 1,093,590; 3,523,698; 3,622,178; 3,874,682; 4,116,315; 4,281,852; 4,345,779; 4,462,612; and 4,466,637, several solutions have been attempted in the field to remedy the foregoing problems.
One such attempted solution to facilitate the proper operation of the landing gear mechanism, is described in U.S. Pat. No. 4,345,779. The patent describes a rotary drive unit which is driven by air under pressure supplied by the towing vehicle. While the use of the rotary drive unit may assist the extension and retraction of the landing gear mechanism, it has further compounded the problems associated with the conventional landing gears. Since the source of pressure for the rotary drive unit is generally the brake line of the towing vehicle, the continuous and frequent use of the hydraulic system of the brakes line, may cause undue strain and wear on the critical portion of the vehicle. Thus, such attempted solution has proven to be less than satisfactory, in that it has increased the danger and risk of injury to the operating personnel, and has not solved the problem of the inadvertent collapse of the landing gear mechanism.
In order to remedy the danger caused by the leak of the brakes line system, attempts have been made to include additional hydraulic devices to operate the landing gear mechanism. This attempted solution is not entirely satisfactory, in that the additional hydraulic devices are relatively bulky and expensive to install, operate and maintain. Also, a large reservoir of hydraulic fluid is required to develop the necessary hydraulic power.
While the various lifting gears, which are disclosed in the foregoing references, may be suitable for some applications, it would be highly desirable to have a new and improved landing gear mechanism and a method of using it, such that the landing gear is less likely to collapse under the load of the trailer, even after repeated use of the gear. Such landing gear mechanism should be simple and safe to operate, and should facilitate the coupling and releasing of the fifth wheel. The inventive landing gear mechanism should also be relatively inexpensive to install on existing structures, to operate and to maintain.